The heart receives its arterial supply from the coronary
arteries , the first branches from the aorta. Its veins drain through
the coronary sinus into the right atrium, or directly into the
chambers.
Flow in the arteries begins at the end of ventricular systole/beginning
of diastole.
The left coronary artery arises from the base of the aorta above the
left cusp (or left posterior). The dilation above the cusp is the aortic
sinus. The artery passes anteriorly and to the left between the left auricle
and the pulmonary trunk. As it reaches the atrioventricular sulcus it divides
into the circumflex artery which continues to the left in the AV sulcus,
and the anterior interventricular artery (LAD) which runs down the surface
of the interventricular septum towards the apex. The anterior interventricular
artery sends branches into the interventricular septum to supply most of
its myocardium, and into the myocardium of the adjacent right and left
ventricle. The circumflex branch continues around the interventricular
sulcus giving off branches to the left ventricle and left atrium. Posteriorly
the circumflex artery anastomoses with branches of the right coronary artery.
In some cases the circumflex artery may supply branches to the SA and AV
nodes.
The right coronary artery is usually smaller than the left, although
right dominance does occur. The artery arises from above the right (anterior)
cusp and passes anteriorly between the right auricle and the pulmonary
trunk to reach the atrioventricular sulcus. As the artery passes to the
right it gives off branches to the right atrium and right ventricle. Posteriorly
it anastomoses with the circumflex branch of the left coronary. The major
branches of the right coronary are the right marginal, posterior
interventricular,
arteries and the branches supplying the SA and AV nodes. The right marginal
is the largest of a group of anterior arteries supplying the right ventricle,
and may reach the apex. The posterior interventricular artery lies on the
interventricular groove and sends branches into the interventricular septum
and adjacent right and left ventricle. The artery to the SA node arises
from the stem of the right coronary to supply the right atrium, SA node
and part of the left atrium. The artery of the AV node arises from the
posterior interventricular as the posterior septal artery supplying the
AV node and interventrucular septum.
Anasatomoses occur between the named branches of the coronary circulation
and between small vessels within the myocardium. The axis of the heart is usually offset to the right
anteriorly and to the left
posteriorly. That is, the left coronary artery supplies part of the right
ventricle anteriorly, together with most of the interventricular septum
and left ventricle while the right coronary supplies the left ventricle
posteriorly, the posterior interventricular septum and most of the right
ventricle. Anastomoses between large vessels occurs at the apex and the
"crux" of the heart. The anterior and posterior interventricular
arteries anastomose around the apex. The right coronary and circumflex
anastomose posteriorly at the "crux", the point where the interventricular
sulcus crosses the line formed by the interatrial and interventricular
septae. Further anastomoses occur within the myocardium around the margins
of the territory of each artery. In young people the extent of this anastomosis
is limited. With age, as the larger vessels succumb to atherosclerosis,
more and more collaterals open up between adjacent territories. However
the extent of anastomoses is usually not sufficient to allow the myocardium
to survive obstruction of a major vessel. The blood supply to the myocardium
is delivered from the epicardial to the endocardial surface. The endocardial
surface is therefore at greatest risk of ischemia. Control of myocardial
vessel calibre is different from that found in the systemic circulation.
Local metabolic factors play a large part, with the level of control varying
from epicardium to endocardium.
Blood drains back into the heart through the coronary sinus , through the anterior cardiac veins and through the venae cordis minimae draining directly into the chambers. The coronary sinus lies in the posterior atrioventricular sulcus. The great cardiac vein accompanies the anterior interventricular artery, draining its territory back towards the atrioventricular sulcus, and passing to the left and backwards to join the coronary sinus. The great cardiac vein receives tributaries from the left atrium and both ventricles. The Middle cardiac vein drains the territory of the posterior interventricular artery into the coronary sinus. The small cardiac vein drains the right side of the right ventricle into the coronary sinus. The anterior cardiac veins drain the anterior part of the right ventricle directly into the right atrium. The venae cordis minimae drain blood from the myocardium directly into all chambers. This route of drainage represents only a very small percentage of venous drainage.
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